The purpose of this R15 application is to study the impact of contextual income inequality, at the US state and county level, on the risk for infant birth mortality. Since infants from African-American and low socioeconomic (SES) groups are more likely to die before their first birthday, we will evaluate whether the mechanisms involved differ across racial and SES groups. The infant mortality rate (IMR) is an estimate of the number of infant deaths for every 1,000 live births. One of the most important and powerful measures of life expectancy in a population is infant mortality. It is a reflection of the economic and social conditions on the health of mothers and newborns, the social environment, individual lifestyles as well as the characteristics and effectiveness of health systems. In 2011, around 24,000 infants died in the United States, resulting in an IMR of 6.1 deaths occurring before the first birthday per 1,000 live births. This rate is high in comparison to other OECD countries. IMR are higher among Blacks, Hispanics, and Native Americans, in comparison to White Americans. Also, IMR are higher among low socioeconomic groups than among moderate and high socioeconomic groups. On top of individual characteristics, the social determinants of health framework posit that the conditions in which people are born, grow, live, work, and age, play an important role in health and well-being. Therefore, contextual exposures, as well as individual level factors need to be addressed. For example, income inequality, or the distribution of wealth in an area such as a US state or county, can play a role in infant mortality. Since most of the studies that investigate the role of income inequality on infant mortality have utilized the ecological study design, results might be biased. Furthermore, contextual income inequality might have a differential impact on infant mortality across racial and socioeconomic groups. Income inequality might have a more detrimental effect on African-Americans and might explain why the IMR is higher among this population group in comparison to White Americans. We propose the following specific aims: 1) To examine the causal association between contextual income inequality and risk for infant mortality; 2) To identify the mechanisms that link contextual income inequality and risk for infant mortality; 3) to test for differential effects of contextual income inequality on risk for infant mortality across racial and SES groups. To achieve these aims, we will conduct novel statistical methods using birth-mortality linked data. We anticipate that findings from this project will improve our understanding of the causes of and mechanisms leading to infant mortality. The proposed study will generate knowledge that is valuable and will inform policy makers and public health professionals to develop and implement policies and programs aimed at lowering the risk for infant mortality, especially among those at greatest risk such as those from African-American or low SES backgrounds.